An aneurysm of the abdominal aorta is a dilatation of the walls of this vessel in the abdominal region. The aorta is the bodies' main artery, ascending from the heart's left ventricle to arch around and descend through the thorax and abdomen to finally divide into the two common iliac arteries that supply blood to the pelvis and lower limbs. Aneurysms usually occur in the abdominal part of the aorta below the kidneys. Failure to treat this condition may eventually result in the rupture of the dilatation (aneurysm) causing a massive hemorrhage in a very short period of time with fatal consequences. This is the reasons that treatments such as implanting a reinforcing prosthesis inside the dilated part of the aorta walls are vital to save patients lives. Despite abdominal aortic aneurysms being the most common, they are not restricted to the abdominal area. Aneurysms may also occur, for example, in the aorta thoracica.
The disruptions caused by of the abdominal aortic aneurysms are very serious and may lead to death. Until recently, treatment of aortic aneurysms consisted of invasive surgery methods for inserting a graft inside the aorta to reinforce the artery. Such a procedure requires a surgical incision to allow access to the vessel, which may result in rupture of the aneurysm due to the sudden reduction in the external pressure exerted by the neighboring organs and tissues which are displaced during access procedure. Quite apart from this serious issue, other risk factors include loss of blood and consequent weakness, aneurysm and low blood pressure associated to the abdominal aortic aneurysm. As a result of the inherent risks and complexity of surgical procedures, several alternative devices and methods have been proposed for implanting a graft inside vessels for the treatment of aneurysms.
However, despite the advances represented by the use of stent and stent-graft devices, they have revealed failings both with regard their implanting processes and performance. As described in U.S. Patent Publication No. US2006/184229, these failings may be classified into four main categories. Type I failings are related to the occurrence of leakage between the vascular endoprosthesis and the vessel walls in the area of the proximal aorta immediately above the aneurysm and, therefore, results in continued blood flow to the aneurismal sac, which thus maintains the pressure at this point and favors continued expansion and consequent rupture of the aneurysm. Type I failings may also be caused by the irregular shape of the vessel and/or calcified topography of the aorta lumen which results in poorly inserted circular prostheses in non-circular lumens of the aorta. Type II failings are related to blood flowing through collateral vessels in the dilated area of the aneurysm which requires a further embolization procedure. Type III failings are of mechanical origin and result from excessive wear of the metal/non-metal interface or the poor integrity of a connection or connections between the modular components of a prosthesis. Lastly, the type IV failings are related to excessive porosity of the prosthesis walls which allows the blood to migrate through the walls despite the soundness of all mechanical seals and connections. To remedy usual Type I failings, US2006/184229 proposes an implantable prosthesis with a radially expandable tubular body with at least one flap extending through it.
U.S. Pat. No. 5,562,724 describes an endovascular graft prosthesis to be positioned in—or close to—a bifurcation of the arterial system of a patient, with this prosthesis comprising a main tubular body having a bag-shape and provided with two outlet openings wherein the said main body is intended for location in the principal upstream artery above the bifurcation and having tubular legs joining the main body and adapted to extend into the two downstream arteries. The positioning of the main body in relation to the radially expansive stent devices and the entire assembly in the arteries is done through the use of guide wires. Although such a device does represent an advance compared to former techniques involving surgical procedures, it still presents failings related to its unfavorable displacement along the blood flow and the precision required when correctly positioning the device at the time of implant. The device described in U.S. Patent Publication No. US2007/027531 also uses a system of guide wires to facilitate the implant operation of the device, which comprises at least one filamentous tubular member having a distal extremity and a proximal extremity with a hollow nucleus to receive the guide wire that helps position the device at the intended location.
U.S. Pat. No. 6,802,859 proposes a bifurcated graft implant having a trunk portion and a portion with independent flexible legs wherein the entire assembly (main portion plus legs) may constitute a unitary body or be formed of modular elements. To ensure the flexibility of the bifurcation, this graft is supported by a stent lattice throughout. Despite this device being self-expanding and having appropriate flexibility at the region of bifurcation, it remains difficult to implant at the intended location.
Another device for the repair of abdominal aortic aneurysms is proposed in U.S. Pat. No. 6,942,691. This device comprises a modular graft that includes two elements configured to be inserted into each other over an extension sufficiently long as to form a resistant seal yet remaining flexible enough to adapt to the region of the bifurcation. The said device comprises a first and second modular element with each expanding from an originally compressed state so as to allow implantation at the intended aneurysm location. The graft described in U.S. Pat. No. 6,942,691 is practical since it allows insertion of both component elements at an intended location but, nevertheless, it presents inconveniences related to the stability of its placement and the relative safety of the large blood flow expected through it.
A solution to facilitate the implant of a device in the region of an aneurysm of the abdominal aorta is proposed in document U.S. Patent Publication No. US2003/120338. This solution relates to providing means to allow the use of a catheter having a very small diameter in the delivery systems for devices within the bodies of patients. The proposed device includes a graft having proximal and distal extremities and is provided with a connector member arranged or fixed at one or both extremities, having one or more connector elements wherein the said connector member may be enclosed within multiple layers of the graft body section. Despite this solution being of interest due to the use of a reduced diameter catheter, this device described in US2003/120338 is complex and presents the disadvantage of being difficult to position correctly at its intended location. A similar device also presenting the same disadvantage is described in document U.S. Patent Publication No. US2006/173533 (corresponding to European Patent No. EP1464301).
To correct the issues of stent graft instability, unwanted displacement from the required position and material fatigue, document WIPO Patent Publication No. WO 2001/67993 proposes a stent graft assembly comprising a main body having an ipsilateral leg and a contralateral stump that, combined, form a bifurcation at the distal extremity. A delivery system for this stent graft assembly is also proposed.
WIPO Patent Publication No. WO 2006/014952 (corresponding to U.S. Patent Publication No. US2006/025850) describes an endoprosthesis comprising (i) a main body having a tubular structure configured to attach firmly to a vessel and serve as a seal preventing blood from reaching the aneurysm, (ii) a section constituted of two legs allowing the passage of fluids to the main body and having multiple stent elements and, (iii) a graft attached to the main body and the two legs. This type of endoprosthesis presents the disadvantage of greater implanting difficulty since it consists of a unitary body insufficiently flexible to adjust well at its intended position.
Another fundamental aspect for the treatment of aneurysms using endoprostheses relates to the methods of implanting these and appropriate means for this delicate operation.
Several delivery systems have been proposed aiming to ensure these features. For example, document U.S. Pat. No. 6,379,372 (corresponding to Brazilian Patent No. PI 9712034) describes a delivery and implant system for use inside a body lumen, e.g., a blood vessel, for a radially expandable endoluminal prosthesis with the said system comprising: (a) a delivery catheter, (b) an introducer assembly, and (c) a dilator. Despite this system allowing the safe introduction of an expandable endoluminal prosthesis, it presents major limitations, such as those relating to providing the means for performing the expansion of the prosthesis in an aneurysm in the vicinity of a bifurcation, i.e., an abdominal aortic aneurysm, as well as preventing the control of fine adjustments required to any of the endoprosthesis components once implanted at the intended location. The delivery devices described in documents U.S. Pat. No. 6,673,102 (corresponding to Canadian Patent No. CA 2503480) and U.S. Pat. No. 6,872,224 (corresponding to Brazilian Patent No. PI 9900959) allow greater flexibility for adjusting the different portions of the endoprostheses at their place of implant and use small diameter catheters but, nevertheless, present the same limitations as the system described in document U.S. Pat. No. 6,379,372.
U.S. Pat. No. 7,112,217 describes a delivery system and method for an endoprosthesis that allows adjustment of the various parts at the place of implant. However, this system and method presents the disadvantage that the link between the main body and the legs of the endoprosthesis is based on the coupling of stents fitted to the extremities of these parts and, furthermore, requires an incision of the artery to introduce the endoprosthesis implanting catheter.
U.S. Patent Publication No. US2001/037142 reveals a delivery system and method for endovascular devices comprising: (i) a first sheath with distal and proximal extremities and at least a first expandable device at the proximal extremity, (ii) a second movable sheath inside the first sheath having respective distal and proximal extremities and containing a second expandable device and (iii) trigger buttons linked to the first and second expandable devices. Despite this system allowing the implant of an endoprosthesis and the adjustment of the various component parts, it neither provides the means of fine adjusting nor correcting the position of the endoprosthesis during the implant operation. The endoprosthesis delivery systems described in WIPO Patent Publication No. WO 01566504 (corresponding to U.S. Patent Publication Nos. US2006/224227 and US 2003/220681) also present the same limitations.
U.S. Patent Publication No. US2006/036314 describes a delivery system for endoprostheses that allows implanting the device in a bifurcated vessel but, however, this system does not allow any means of fine adjusting or correcting the position of the endoprosthesis during the implant operation.
U.S Patent Publication No. US2006/085012 illustrates a procedure for implanting an endoprosthesis using a delivery system without, however, describing implanting in a bifurcated vessel which is an operation requiring further steps for expanding the different parts of the endoprosthesis, such as, for example, the main body and the legs extending into the arteries branching from the trunk vessel in which the main body of the endoprosthesis is located. The delivery system described in document U.S. Patent Publication No. US2006/142836 also presents similar failings. However, the delivery system described in U.S. Patent Publication No. US2006/276872 (corresponding to PI 0414109) is intended for implanting this type of device in a curved vessel, i.e., the arched part of the aorta, where guide wire type delivery systems such as those described in documents WIPO Patent Publication Nos. WO 02051336 and WO 2005/039442 cannot be used. Despite the system described in US2006/276872 being appropriate for curved sections of vessels such as the aorta, it does not meet the requirements for implanting endoprostheses in the vicinity of bifurcations and neither provides a means for correcting the position of the endoprosthesis during the implant process.
Although the endoprostheses and implanting systems mentioned above represent significant advances, mainly since they replace surgical techniques, it remains necessary to improve these devices as well as the methods for implanting them and applying them to varying biological conditions.